The invention relates to a base station for a radio communications system, in particular for mobile radio networks.
In radio communications systems, messages (for example voice, image information or other data) are transmitted over a radio interface using electromagnetic waves. The radio interface relates to a connection between a base station and mobile stations, it being also possible to supply fixed radio stations instead of the mobile stations. The electromagnetic waves are emitted here using carrier frequencies that lie in the frequency band provided for the respective system. In the case of the global system for mobile communication (GSM), the carrier frequencies lie in the region of 900, 1800 or 1900 MHz. For future radio communications systems, for example the universal mobile telecommunication system (UMTS) or other third generation systems, frequencies in the approximately 2000 MHz frequency band are provided.
European Patent Application EP 0 560 388 A1 (which corresponds to U.S. Pat. No. 5,321,690) discloses a base station which contains for a time division multiple access (TDMA) transmission method a multiplicity of transceiver devices which are connected to central devices, for example interface devices, over a common bus system. Traffic data and control data are transmitted in parallel here.
The length of the lines of the bus structure reduces the possible data rate of a transmission over the bus structure owing to the physical properties of the lines. Furthermore, it is necessary to provide identical lengths for the various lines in order to ensure that the functioning of the bus is physically correct. This gives rise to considerable expenditure because in digital systems each bit must arrive at a receiving module at a particular time.
U.S. Pat. No. 5,555,260 discloses a base station of a cellular mobile radio system which has a point-to-point connection for respective connections between a central amplifier interface and amplifier devices disposed inside or outside the base station.
International Patent Disclosure WO 97/33388 discloses a distributed microcellular communications system in which a macro-cell is divided into a multiplicity of so-called subcells. The subcells are supplied by in each case one remote station for communication with mobile stations, the station being connected to a central base station.
It is accordingly an object of the invention to provide a base station for a radio communications system that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the transmission of traffic data from and to the transceiver devices is improved.
With the foregoing and other objects in view there is provided in a radio communications system, in accordance with the invention, a base station, including:
a least one transceiver device having at least one interface device;
at least one central unit for controlling the base station and having at least one interface device; and
at least one individual line for connecting the interface device of the transceiver device to the interface device of the central unit in accordance with a point-to-point connection for transmitting traffic data, the interface device of the transceiver device and the interface device of the central unit configured for propagation time measurement of a transmission over the individual line;
at least one of the transceiver device and the central unit having a synchronization device based on the propagation time measurement.
A base station according to the invention for a radio communications system contains at least one carrier-related transceiver device and at least one central unit for controlling the base station. The transceiver device in this case processes signals of at least one frequency channel on whose carrier frequency tuning is carried out in terms of frequency during transmission and/or reception.
The transceiver device and the central unit each contain at least one interface device which are connected by at least one individual line in accordance with a point-to-point connection for transmitting traffic data. Therefore, in accordance with the prior art according to U.S. Pat. No. 5,555,260, point-to-point connections with individual lines for each transceiver device which do not need to satisfy the requirements of identical lengths are used instead of a bus structure. In this way, an essentially more cost-effective implementation of the transmission of traffic data between the central unit and transceiver device is possible because the data rate can also be increased in accordance with the length of the individual line. When there are a plurality of transceiver devices, they can be distributed spatially as desired.
A logic bus structure is mapped onto physical point-to-point connections. Traffic data, oandm (operations and maintenance) data and also synchronization data can be transmitted using the logic bus structure. The base station is suitable for use in radio communications systems with GSM, TDMA, CDMA radio interfaces, or other radio interfaces.
Furthermore, the interface devices are characteristically configured for propagation time measurement of the transmission over the individual connection. Synchronization devices based on propagation time measurements are provided in the transceiver device and/or central unit. The synchronicity of a plurality of transceiver devices is ensured by measuring and taking into account the signal propagation time on the individual line. If the accuracy of the measurement is sufficient, it is possible to dispense with wider-ranging synchronization. The measurement of the propagation time can be carried out here at one end or at both ends of the individual line.
According to one advantageous development of the invention, the central unit has a plurality of interface devices that are connected to one another by use of short lines. The central unit is composed of one or more circuit boards that are distinguished by small physical size. This reduced size permits rapid and comparatively easily implemented communication within the central unit, while the data that are intended for the respective transceiver device are transmitted over the individual lines. The memories are advantageously provided for the interface devices so that the traffic data are buffered. In this way, the interface devices perform buffering in order to adapt transmission protocols between a transceiver device and the central unit and/or within the modules.
According to a further advantageous embodiment of the invention, the interface devices are configured in such a way that the traffic data are transmitted serially. This saves line costs and avoids problems of identical length within a connection between the central unit and a transceiver device. The individual line is advantageously formed by a pair of lines (twisted pair) for each transmission direction.
It is also possible to transmit clock information and/or control information together with the traffic data. Furthermore, the interface devices are advantageously configured to transmit information for baseband hopping between the transceiver devices. This applies in particular to the connection in the downlink direction. Not only the traffic data but also further information are therefore transmitted by the point-to-point connection. The aforesaid advantages then apply also to this transmission. According to a further embodiment of the invention, real-time information and information for which timing is uncritical are transmitted over the individual connection. The high data rate that can be achieved by the star-shaped structure of the communication between the central unit and transceiver devices permits the various information items to be combined in one transmission protocol. The quantity and order of the transmitted information is restricted by the maximum value of the capacity of the point-to-point connection and by the capacity of the bus on the central unit. If necessary, the quantity of information transmitted can be made to approach this maximum value.
Furthermore, it is possible to provide that a plurality of interface devices of the central unit are connected to one another with a bus structure. The small physical size of the central unit permits a bus structure to be used even with very high data rates, so that the bus structure within the central unit advantageously contains separate lines for real-time information and for information for which timing is uncritical. The respectively most economical solutions can thus be selected for the respective data stream.
According to one development of the invention, the interface devices are configured to transmit with a frame-oriented protocol. The order of the information to be transmitted is defined by the frame protocol. The significance of individual data is thus defined and does not need to be additionally signaled. The timing pattern of the frame-oriented protocol is advantageously oriented according to the timing pattern of a PCM transmission. Because the PCM transmission between the base station and further network-end components of the radio communications system is used for a multiplicity of radio interface standards, the base station according to the invention can easily be adapted to these standards.
In order to improve the transmission security, there may be provision for a synchronization signal to be transmitted from the central unit to the transceiver device. The synchronization signal can be transmitted from one interface to the other interface of the central unit to the transceiver device. Such a synchronization signal can be set individually for each of the transceiver devices, as a result of which even different radio interface standards can be used. A master pulse of the central unit can thus control the transmission of the transceiver device and its clocking. Additionally, the synchronization signal can be adjusted individually for a plurality of transceiver devices.
According to a further development of the invention, the transceiver device is one of a plurality of transceiver devices that use different radio interface standards.
In order to ensure satisfactory operation of the base station in the event of failures of the central unit, the base station can advantageously contain a second central unit which is additionally connected to the transceiver devices by at least a second individual line in accordance with the point-to-point connection. This produces redundancy that permits switching over to the second central unit without the base station failing for a relatively long time.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a base station for a radio communications system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.